The field of the invention relates generally to thermal limiter devices, and more specifically to a thermal limiter fuse system for thermally protecting a multi-phase electric motor application in a loss of phase condition.
Electric motors operating in severe thermal duty conditions present certain challenges from a circuit protection perspective. For example, electric motor drives for hydraulic pumps in aerospace applications are designed to operate in severe thermal duty conditions. Circuit protection devices for protecting the motor drives such as overcurrent protection fuses and circuit breakers are likewise designed to withstand severe thermal duty conditions. Conventional overcurrent protection are designed primarily to respond to overcurrent fault conditions (e.g., short circuit or overload conditions) and work quite well to protect the motor in this regard, but problematic operating conditions of motor drives may arise that do not involve overcurrent conditions that trigger operation of overcurrent protection devices, and conventional overcurrent protection devices therefor are incapable of addressing them.
Specifically for multi-phase electric motors, if one of the power phases supplied to the motor is lost while the motor is operating, the motor may continue to operate but is subject to overheating. If not accompanied by an overcurrent condition, overcurrent protection devices will not respond to open the circuit and interrupt the motor. Coupled with severe thermal duty conditions, unacceptable fire hazards may result. A thermal protection device and system that is responsive to a loss of phase condition in a multi-phase electrical motor application and in the absence of an overcurrent condition is accordingly desired.